Non-linear, optically active chromophores have second-order effect in optical switching, frequency conversion, and electrooptical modulation, to name a few applications. These compounds are also effective in third order practical applications such as optical switching, amplification, beam steering and clean-up, and image processing.
In order to be effective, most non-linear, optically active chromophores have a general chemical structure: EQU A--Y--Z--Y--B
wherein A is an electron donating group, B is an electron withdrawing group, Y is a group possessing a delocalizable electron system (e.g. a benzene ring), and Z is either a divalent atom with a polarizable electron lone pair (e.g. a sulfur atom) or a .pi.-system (e.g. a carbon-carbon double or triple bond). The polarizable electrons of the Z moiety and the delocalizable .pi.-electrons of the Y moiety serve as a bridge facilitating communication between the A and B groups. This maintains what is known as the "push-pull" effect. Various compounds have been disclosed that exhibit these characteristics:
U.S. Pat. No. 1,965,776 to Lantz discloses sulfides of nitroaminodiphenyl or substitution products thereof which are represented by the general formula: EQU NO.sub.2 (2 or 4)--R--S--R'--NH.sub.2 (2' or 4')
in which R and R' are benzene nuclei that may or may not be substituted.
U.S. Pat. No. 5,075,409 to Barthelemy et al. discloses polymeric materials containing non-linear, optically active chromophores having the general formula: ##STR3## wherein R.sub.1 and R.sub.2 may be the same or different and denote a linear or branched methylenic chain containing preferably from 2 to 6 carbon atoms; R.sub.3 is an aliphatic, aromatic, or arylaliphatic hydrocarbon radical; R.sub.4 and R.sub.5 may be the same or different and denote a nitrogen atom or the CH radical or are both carbon with the R.sub.4 --R.sub.5 bond being a double or triple bond; Z.sub.1 and Z.sub.2 are either the same or different and denote an aromatic group, wherein Z.sub.1 optionally contains one or more substituents R.sub.7 and wherein Z.sub.2 optionally contains one or more substituents R.sub.7 in addition to group A; each substituent R.sub.7 independently maybe a lower alkyl, halogen, amido, amino, sulfoxide, hydroxyl radicals, alkoxy or trifluoromethyl group; and A denotes an electron acceptor group, it being possible for Z.sub.2 to carry one or more A groups, with nitro and cyano groups being the preferred electron acceptor A groups.
The above prior art summaries are merely representative of portions of the inventions disclosed in each reference. In no instance should these summaries substitute for a thorough reading of each individual reference. All of the above references are hereby incorporated by reference.
The substances disclosed in the references cited above lack the surface area necessary for greater efficiency in interacting with incoming radiation. Additionally, in cases where the chromophore is bound to a polymer carrier, it is advantageous to increase the relative amount of the non-linear, optically active moiety in order to increase the optical activity of the complete polymer matrix.
Another problem in the complete polymer matrix, often referred to as the "host-guest" system, is that these systems have the disadvantage of residual mobility of the chromophore. This residual mobility means the chromophore lacks the ability to maintain orientation and hence polarization over time, upon electric field poling. Therefore it is desirable to increase the size of the chromophore thereby increasing the bulkiness and reducing the residual mobility. From the reduction in residual mobility, the capability of the polymer matrix to maintain orientation is increased as is polarization upon electric field poling.